1. Field of the Invention
The present invention relates to sputter targets and sputter target assemblies having a uniform distribution of the magnetic leakage flux.
2. Description of Related Art
Cathode sputter targets and target assemblies are widely utilized for the deposition of thin layer materials onto wafer substrates and subsequent circuit patterns laid thereon. The process requires a gas ion bombardment of a target having a surface formed of a material that is desired to be deposited onto a substrate. The target forms part of a cathode assembly that, together with the anode, is placed in an evacuated chamber filled with an inert gas, such as argon. A high voltage electrical field is applied across the cathode and the anode. The inert gas is ionized by electrons ejected from the cathode. Positively charged gas ions are attracted to the cathode, and upon impingement with the target surface, these ions dislodge the target material. The dislodged target material traverses the evacuated chamber and deposits as a thin film on the desired substrate, which is usually located in close proximity to the anode.
To further increase sputtering the concurrent application of an arch-shaped magnetic field superimposed over the electrical field has been utilized. This method is known as a magnetron sputtering method. The arch-shaped magnetic field traps electrons in an annular region adjacent to the target surface, thereby increasing the number of electron-gas atom collisions in the area to produce an increase in the number of positive gas ions (i.e., plasma) in the region that strike the target to dislodge the target material.
For magnetron sputter targets, the magnetic leakage flux (MLF), also known as magnetic pass through flux (PTF) at the target surface must be high enough to ignite and sustain the plasma. Under normal sputtering conditions, the higher the magnet strength, the higher the MLF. In the case of ferromagnetic materials, however, the strength of the high intrinsic permeability of the material effectively shields or shunts the magnetic field from the magnets behind the target and hence reduces the MLF on the target surface.
Considering the importance of the magnetic properties of sputter targets, manufacturers have relied upon various techniques to fabricate sputter targets with lower sputter target permeability and an increased PTF.
U.S. Pat. No. 4,401,546 discloses a planar ferromagnetic segmented target, where the segments are separated by gaps through which the magnetic field leaks to produce an MLF of 200 Gauss on the surface of the target.
U.S. Pat. No. 5,827,414 discloses a planar ferromagnetic target having a certain thickness due to the gaps in the target. The gaps in this configuration are radial gaps formed by slots in the target body that are perpendicular to the flux of the magnetron, thereby producing a more effective and homogeneous leakage magnetic field on and parallel to the surface of the target body so that the sputtering plasma density may be increased.
Other techniques developed include the hot or cold working of the sputter target blank to increase the PTF by manipulating the crystallographic structure. European Patent Document No. 799905 recognized that strain can manipulate a high-purity cobalt target's permeability. This patent publication discloses a process that relies upon either cold or warm rolling to reduce the target's initial permeability parallel to the target's surface to about 7. However, this process increases the permeability perpendicular to the target's surface.
U.S. Pat. No. 5,766,380 discloses a cryogenic method for fabricating aluminum alloy sputter targets. This method uses cryogenic processing with a final annealing step to recrystallize the grains into a desired texture. Similarly, U.S. Pat. No. 5,993,621 utilizes cryogenic working and annealing to manipulate and enhance crystallographic texture of titanium sputter targets.
Unfortunately, these processes have limited success with respect to the limited target thickness and control of the target's final magnetic properties, which in turn negatively affects the deposition rates and the film uniformity.
To meet the requirements of the semiconductor manufacturing industry and to overcome the disadvantages of the related art, it is an object of the present invention to provide a ferromagnetic sputter target and assembly with a uniform MLF.
It is also an object of the invention to provide a method of forming said ferromagnetic sputter target and assembly.
It is another object of the invention to provide an increased target thickness uniformity.
As a result of the invention, the target life is increased, and the cost of manufacturing the wafers is decreased. In addition, the film deposited onto the substrate has an increased uniformity.
Other objects and advantages of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.